1. Field of the Invention
This invention relates in general to pumps and, more particularly, to an improved fluid pump for producing oil-bearing formations, and specifically sucker rod-operated fluid pump for oil wells.
2. Description of Prior Art
A conventional oil well includes a cased well bore with one or more strings of tubing extending downwardly through the casing into the oil or other petroleum fluid contained in the subsurface mineral formation to be produced. The casing is perforated at the level of the production zone to permit fluid flow from the formation into the casing, and the lower end of the tubing string is generally open to provide entry for the fluid in the tubing.
One type of pump conventionally employed in structures of the type described is wedged into an internal constriction or seating nipple formed internal of the tubing below the fluid level. A metallic enlargement on the external body of the pump prevents it from traveling below the seating nipple and resilient seal rings on the body of the pump housing act to form a leak-proof seal between the seating nipple and pump. The pump is generally driven by a mechanical linkage of metal rods, referred to in the trade as sucker rods which extend from the pump to the well surface. The sucker rod linkage is powered in a reciprocating motion by a conventional mechanical apparatus usually called a pumping unit located at the well surface.
The conventional pump itself generally includes a housing through which a piston is reciprocated by the sucker rod linkage. In its simplest form, the conventional pump of the type described often includes a number of ball and seat valves with one such valve associated with the piston or plunger (traveling valve) and another (standing valve) at the inlet port of the housing or barrel of the pump. On the upstroke of the plunger, the ball in the inlet port valve or standing valve is drawn away from its seat and the ball of the outlet port valve or traveling valve is forced over its seat to draw fluid from below the seating nipple and into the housing. On the piston downstroke, the ball in the standing valve is forced onto its seat and the ball in the traveling valve moves away from its seat to allow the plunger to move downwardly through the fluid contained in the housing. On the subsequent upstroke, the closing of the traveling valve forces the fluid above the plunger out of the housing through the outlet ports and into the tubing above the seating nipple and simultaneously fills the housing below the plunger with fluid. Repetition of this cycle eventually fills the tubing string and causes the fluid to flow to the surface.
Ball valve pumps are also relatively limited in theoretical efficiency and cycling rate due to their inherent principle of operation. Any increase in the amount of fluid which can be produced by such a pump usually involves an increase in the driving power and pump dimensions and includes a corresponding decrease in efficiency. Moreover, the valve closure time required for the ball and seat type valves restricts the speed of the pumping cycle and thereby further limits the maximum product on rate of pumps employing these valves.
In operation of a sucker rod pump, the plunger in the barrel is lifting the entire column of oil above the plunger on the upstroke. Thus, the load on the plunger is equal to the weight of the column of oil having a cross-sectional area of the pump plunger. The cross-sectional area of the pump plunger times the depth of the oil well equals the volume of oil being lifted.
The efficiency and effectiveness of the pump depends upon a very close fit between the exterior plunger pump surface and the barrel interior cylindrical surface. When fluid leakage occurs between these surfaces, efficiency of the pump is reduced and if substantial fluid flow occurs between the exterior plunger surface and the interior barrel, the pump can become totally defective. The problem of pumping crude oil is that in some locations substantial components of sand or other abrasives are entrained within the crude oil fluid. Most oil producing formations are of relatively high porosity and are formed of compacted sand granules, and some of the sand granules become dislodged from the formation as the fluid is extracted from it. Abrasives also originate from scale, mineral deposits and other sources. Since most reciprocating downhole pumps are made of metal, that is, a metal barrel and a metal plunger, there is metal to metal contact as the plunger is reciprocated within the barrel. If sand is entrained within the crude oil fluid, the abrasive effect can soon wear a pump plunger to the point where the well efficiency drops below an acceptable level. The traveling valve in most sucker rod pumps has a housing that is less than the internal diameter of the barrel and consequently permits fluids to gather around in between the traveling valve housing and the barrel exacerbating the abrasion problems.
Various arrangements of pumps have been suggested in the prior art to overcome the various problems associated with sucker rod pumps for oil wells. U.S. Pat. No. 5,141,416 to Cognevich et al describes a method of manufacturing a plunger for a downhole reciprocating oil well pump. A cylindrical material plunger has its outer surface machined and then is prepared by grit-blasting to receive a coating of ceramic and then the ceramic outer surface is ground to the proper plunger design diameter. Cognevich et al is providing a surface that is longer wearing than the original material surface of the plunger.
U.S. Pat. No. 5,009,000 to Wilmeth et al describes a method of hardening the plunger by forming a boronized case on the plunger. The plunger additionally includes circumferential grooves which tend to trap abrasive particles and help equalize hydrostatic pressure around the plunger.
U.S. Pat. No. 4,968,226 to Brewer describes a plurality of openings formed in the midportion of the pump barrel. These openings allow fluid from the tubing string to enter the intake chamber of the barrel during a portion of the upstroke permitting equilibration of the pressure differential therebetween. Further Brewer provides a traveling valve with a substantially reduced outside diameter which permits fluid around the outside diameter traveling valve cage which permits fluid around its outer surface between the pump barrel and the traveling valve cage. A plunger, sized for substantially fluid tight reciprocation relative to the barrel, is received in the barrel. The plunger has a top with an opening therein and a bottom with an opening therein, and a body. The body defines a cavity continuous with the openings in the top and bottom of the plunger. The length of the plunger is substantially less then the length of the barrel. The plunger has an end portion which, with a portion of the barrel cavity, defines a fluid intake chamber. The volume of the fluid intake chamber therefore varies with reciprocal movement of the plunger and the barrel. A valve associated with the plunger is included for permitting fluid to flow through the plunger only in an upward direction. The openings in the midportion of the barrel cooperate with the relative lengths of the barrel and the plunger to prevent fluid communication between the conduit and the fluid intake chamber during a first phase of the extension stroke and to permit communication between the conduit and the fluid intake chamber during a second phase of the extension stroke.
U.S. Pat. No. 4,662,831 to Bennett discloses a pump for lifting liquids from a well in an earth formation and concurrently fracturing the earth formation. This is accomplished using a pump of the reciprocating piston variety and providing a first valve that permits a quantity of the liquid to be gathered on the downstroke of the pump and lifted during the upstroke of the pump and a second valve that permits a portion of the formation liquids to be forced back in to the earth formation during a first portion of the downstroke of the pump and that prevents further passage of fluids back in to the formation during a second portion of the downstroke of the pump. Also, a third valve for venting formation gases from the interior of the pump near the top of the pump upstroke in order to prevent cushioning of the force of the pump downstroke due to the compressibility of such gases.
U.S. Pat. No. 3,697,199 to Spears discloses a slave valve pump. The pump employs a first piston which is directly moved by an external power source and a slave piston which is moved by the resulting pressure differentials created by the movement of the first piston. The first or lower piston is fixed to the lower end of a cylindrical rod and the upper piston has a tubular form and is adapted to slide over the rod. The axial movement of the upper piston is controlled by the resulting pressure differential crested across its length. The pressure differential acts to move the upper piston to appropriately open or close the outlet ports of the pump which in turn permits fluid to be expelled through the outlet ports and prevents return flow into the pump. On the downstroke of the lower piston, a reduced pressure is created between the slave piston and the lower piston which permits fluid flow into this low pressure area between the two pistons which the lower piston moves past inlet ports and fluid is forced through the inlet ports to the low pressure area.
The problem with the API standard pumps prevalent throughout the oil industry is that the pumps are confronted with pumping fluids and gases drawn into the barrel of the pump and whatever abrasive particles, such as quartz or sand, brought into the pump on the upstroke will be forced to move around in the barrel and around the outer surface of the traveling valve on the downstroke which causes abrasion, and in some instances the gas will collect and compress and cause gas lock to occur. Certainly hardening the plunger will assist in reducing the amount of wear on the plunger and perhaps leakage past the plunger.
The object of the present invention is to provide a pump in which the outside diameter of the traveling valve body is of comparable outside diameter as the plunger.
It is a further object of the present invention to provide an improved downhole pump in which the stationary valve is placed within the upper threaded area of the barrel cage and where the traveling valve is placed in the lowermost portion of the plunger cage, thus reducing the distance between the traveling valve and the stationary valve at the bottom of the downstroke of the plunger.
It is a further object of the present invention to provide an improved downhole pump which is of a lesser length or longer stroke by providing a stationary valve in the upper threaded area of the barrel cage and the traveling valve is placed in the lowermost portion of the portion of the closed plunger cage, thus reducing the distance between the traveling valve and the stationary valve at the bottom of the downstroke of the plunger.